Often used in process measurement and automation technology for measuring flow velocities, respectively volume, or mass, flow rates corresponding to the flow velocity (u), of fluids flowing in pipelines, especially rapidly flowing, and/or hot, gases and/or fluid flows of high Reynolds number (Re), are measuring systems embodied as vortex flow measuring devices. Examples of such measuring systems are known from, among others, Japanese Patent JP-A 2005227115, Japanese Patent JP-A 9196720, U.S. Pat. No. 3,587,312, U.S. Pat. No. 4,562,745, U.S. Pat. No. 5,463,904, U.S. Pat. No. 6,101,885, U.S. Pat. No. 6,298,734, U.S. Pat. No. 6,752,027 and U.S. Pat. No. 7,073,394. These disclosed measuring systems each have a bluff body protruding into the lumen of the respective pipeline, consequently flowed against by the fluid, for producing vortices lined up in a so-called Karman vortex street in the volume portion of the fluid flow flowing directly downstream from the bluff body. The vortices are, as is known, generated on the bluff body with a shedding rate (1/fVtx) dependent on the flow velocity and ideally proportional to the flow velocity. Furthermore, the measuring system includes, integrated in the bluff body, respectively associated therewith or located downstream therefrom, namely in the region of the Karman vortex street and protruding into the flow, a transducer element. The transducer element—most often embodied with paddle shape—serves to produce a sensor signal, which corresponds to pressure reigning within the fluid and exhibiting, as a result of the Karman vortices, periodic fluctuations, consequently a signal frequency (˜fVtx) corresponding to the shedding rate of the vortices. According to this, prerequisites for the desired proportionality of flow velocity and vortex shedding rate—described, as is known, via the Strouhal number (St˜fVtx/u)—are an as high as possible Reynolds number of above 20000 as well as an initially as undisturbed as possible, steady, flow profile in the region directly before the bluff body. Thus, for measuring systems of the aforementioned type, usually approach lengths of more than 10 times the nominal diameter of the pipeline are recommended.
For pipelines of large nominal diameter, namely DN 100 (inner diameter=100 mm) or larger, because of the otherwise very complicated bluff body, frequently so-called “insertion type”, vortex, flow measuring devices are used, namely measuring systems of the aforementioned type, in the case of which, such as, for example, also shown in the already mentioned JP-A 2005227115, JP-A 9196720, U.S. Pat. No. 4,562,745, respectively U.S. Pat. No. 6,752,027, bluff body and transducer element are integrated together in a sensor module insertable externally through the pipe wall of the pipeline, consequently a sensor module built essentially shorter than the nominal diameter. The sensor module is, furthermore, connected with an electronics module—most often an electronics module releasably connected therewith and/or encapsulated pressure and shock resistantly, in given cases, also outwardly hermetically sealed. Electronics modules for industrially usable measuring systems have usually, electrically connected with the transducer element via connecting lines, in given cases, with interposing electrical barriers and/or galvanic separation locations, a corresponding transmitter electronics for processing the at least one sensor signal produced by the transducer element and for producing digital measured values for the respectively to be registered, measured variable, namely flow velocity, volume flow rate and/or mass flow rate. The transmitter electronics, which is usually accommodated in an electronics housing of metal and/or shock resistant, synthetic material for industrially usable measuring systems, respectively measuring systems established in industrial measurements technology, includes additionally most often also standard, external interfaces embodied, for example, as two conductor connections, respectively as interfaces compatible with established fieldbusses, for communication with superordinated measuring and/or control systems formed, for example, by means of programmable logic controllers (PLC).
In order, in the case of such measuring systems depending most often still more on undisturbed and steady, consequently largely determined, flow profiles, combined with as short as possible approach length, to be able to achieve a sufficient accuracy of measurement, there is integrated in their respective sensor modules, at times, supplementally, a flow conditioner, for instance, in the form of a straight tube providing a defined flow path and having a smaller caliber than the pipeline. The tube is aligned with the pipeline, and the bluff body and the transducer element are placed, in the lumen of the tube.
A disadvantage of conventional “insertion type”, vortex, flow measuring devices is that, because of the desired short approach length, on the one hand, and because of the bore most often having standard dimensions, on the other hand, always a compromise must be made between the effectiveness of the flow conditioner, respectively the installed dimensions of the sensor module influencing this, not least of all, however, installed dimensions predetermined by the bore, and the accuracy of measurement actually achievable for the flow measuring device formed by means of the respective sensor module.